The amount of electricity that a power plant generates depends on its electricity generation capacity and on the amount of time the individual generators at a power plant operate at a specific capacity. For example, if a power plant with a single generator that has an electricity generation capacity of 100 Megawatts (MW) operates at that capacity continuously for 24 hours, it will generate 2,400 megawatthours (MWh) of electricity. If the power plant operates at that capacity continuously for 365 days, it will generate 876,000 MWh.
Most power plants do not operate at full capacity every hour of every day of the year, and for many, their electricity generation capacity is different in summer and winter months because of seasonal variations in the temperature of generator cooling fluid (water or ambient air). There are three categories of electricity generating capacity: nameplate capacity, net summer capacity , and net winter capacity.
A measure of electricity generation capacity relative to electricity generation is capacity factor. The U.S. Energy Information Administration (EIA) publishes the average monthly and annual capacity factors for utility-scale electric power generators, which have a nameplate generation capacity of at least 1 MW, for generators primarily using fossil fuels and for generators not primarily using fossil fuels in Tables 6.07A and 6.07B respectively of the Electric Power Monthly. Details on how EIA calculates capacity factor are included on page 21 of the Electric Power Monthly Technical notes.
Nuclear power reactors have the highest average monthly and annual capacity factors because they usually operate at or near their rated electricity generating capacity throughout the year to provide base-load electricity generation. U.S. nuclear power plants reduce generation to refuel every 18 to 24 months, mostly in fall and spring when electricity demand is lower. Coal-fired power plant capacity factors have declined over time largely because of increases in natural-gas and renewable energy use for electricity generation. Petroleum-fueled power plants have the lowest average monthly and annual capacity factors on a national level because they are generally operated to supply electricity during periods of very high electricity demand. (Exceptions are Hawaii, where petroleum fuels are major electricity generation sources, and in remote villages in Alaska that are supplied by diesel-fueled electricity generators.) Geothermal and biomass-fired power plants have the highest capacity factors among renewable power plants because their energy sources are relatively constant. Hydroelectric generation is affected by precipitation levels that vary seasonally. Wind and solar power plant electricity generation and capacity factors are determined by availability of wind and solar energy on a daily and seasonal basis.
What is the difference between electricity generation capacity and electricity generation?
What is the efficiency of different types of power plants?
Does EIA have data on each power plant in the United States?
Capacity factors for utility scale generators primarily using fossil fuels
Capacity factors for utility scale generators not primarily using fossil fuels
U.S. nuclear generation and generating capacity (historical monthly capacity and generation by state and reactor)
Electricity generation, capacity, and sales in the United States
Nuclear energy (historical monthly and annual data on the total number of U.S nuclear reactors, electricity generation capacity, electricity generation, and capacity factors)
Revised and updated: August 17, 2023.